generate filename of value and extend

[Marre]

from PIL import Image
import sys

rr = input('R > code: ')
gg = input('G > code: ')
bb = input('B > code: ')
 
filename = ( str(rr)+str(gg)+str(bb)  )
suffix =  ".png"

im.save("/home/marre/XY-Kordinaterna/PAINT_BILDER/filename + suffix")

#----------------------------------------------------------------------------
inserted values to the program

R > code: 1
G > code: 2
B > code: 3

my result: filename + suffix = 123.png

I get a error message that i cant understand

Error:
Traceback (most recent call last):
  File "/home/marre/XY-Kordinaterna/4_från_cluster_EN_FÄRG_test.py", line 48, in <module>
    im.save("/home/marre/XY-Kordinaterna/PAINT_BILDER/filename + suffix")
  File "/usr/lib/python2.7/dist-packages/PIL/Image.py", line 1662, in save
    format = EXTENSION[ext]
KeyError: ''

I an greatfull for help
br Marre